Peripheral venous blood oxygen saturation can be non-invasively estimated using photoplethysmography

Measurement of peripheral venous oxygen saturation (SvO
2
) is currently performed using invasive catheters or direct blood draw. The purpose of this study was to non-invasively determine SvO
2
using a variation of pulse oximetry techniques. Artificial respiration-like modulations applied to the peripheral vascular system were used to infer regional SvO
2
using photoplethysmography (PPG) sensors. To achieve this modulation, an artificial pulse generating system (APG) was developed to generate controlled, superficial perturbations on the finger using a pneumatic digit cuff. These low pressure and low frequency modulations affect blood volumes in veins to a much greater extent than arteries due to significant arterial-venous compliance differences. Ten healthy human volunteers were recruited for proof-ofconcept testing. The APG was set at a modulation frequency of 0.2 Hz (12 bpm) and 45–50 mmHg compression pressure. Initial analysis showed that induced blood volume changes in the venous compartment could be detected by PPG. Estimated arterial oxygen saturation (97% [IQR=96.1%–97.4%]) matches published values (95%–99%). Estimated venous oxygen saturation (93.2% [IQR=91.–93.9%]) agrees with reported ranges (92%–95%) measured in peripheral regions. The median difference between the two saturations was 3.6%, while the difference between paired measurements in each subject was statistically significant (p=0.002). These results demonstrate the feasibility of this method for real-time, low cost, non-invasive estimation of SvO
2
. Further validation of this method is warranted.